1. Field of the Invention
The present invention relates to the processing of workpieces such as semiconductor wafers, and in particular to an integrated system for workpiece handling and inspection at the front end of a tool associated with a semiconductor process.
2. Description of Related Art
A SMIF system proposed by the Hewlett-Packard Company is disclosed in U.S. Pat. Nos. 4,532,970 and 4,534,389. The purpose of a SMIF system is to reduce particle fluxes onto semiconductor wafers during storage and transport of the wafers through the semiconductor fabrication process. This purpose is accomplished, in part, by mechanically ensuring that during storage and transport, the gaseous media (such as air or nitrogen) surrounding the wafers is essentially stationary relative to the wafers, and by ensuring that particles from the ambient environment do not enter the immediate wafer environment.
A SMIF system has three main components: (1) minimum volume, sealed pods used for storing and transporting wafers and/or wafer cassettes; (2) an input/output (I/O) minienvironment located on a semiconductor processing tool to provide a miniature clean space (upon being filled with clean air) in which exposed wafers and/or wafer cassettes may be transferred to and from the interior of the processing tool; and (3) an interface for transferring the wafers and/or wafer cassettes between the SMIF pods and the SMIF minienvironment without exposure of the wafers or cassettes to particulates. Further details of one proposed SMIF system are described in the paper entitled “SMIF: A TECHNOLOGY FOR WAFER CASSETTE TRANSFER IN VLSI MANUFACTURING,” by Mihir Parikh and Ulrich Kaempf, Solid State Technology, July 1984, pp. 111-115.
Systems of the above type are concerned with particle sizes which range from below 0.02 microns (μm) to above 200 μm. Particles with these sizes can be very damaging in semiconductor processing because of the small geometries employed in fabricating semiconductor devices. Typical advanced semiconductor processes today employ geometries which are one-half μm and under. Unwanted contamination particles which have geometries measuring greater than 0.1 μm substantially interfere with 1 μm geometry semiconductor devices. The trend, of course, is to have smaller and smaller semiconductor processing geometries which today in research and development labs approach 0.1 μm and below. In the future, geometries will become smaller and smaller and hence smaller and smaller contamination particles and molecular contaminants become of interest.
SMIF pods are in general comprised of a pod door which mates with a pod shell to provide a sealed environment in which wafers may be stored and transferred. So called “bottom opening” pods are known, where the pod door is horizontally provided at the bottom of the pod, and the wafers are supported in a cassette which is in turn supported on the pod door. It is also known to provide front opening pods referred to as front opening unified pods, or FOUPs, in which the pod door is located in a vertical plane, and the wafers are supported either in a cassette mounted within the pod shell, or to shelves mounted in the pod shell.
During the fabrication of semiconductor wafers, the SMIF pods are used to transport the workpieces between various tools in the wafer fab. These tools include process tools for forming the integrated circuit patterns on the wafers, metrology tools for testing the wafers, sorters for sorting and rearranging the wafers within one or more SMIF pods, and stockers for large scale storage of the SMIF pods. The tools are generally laid out in a wafer fab in one of two configurations, a bay and chase configuration or a ballroom configuration. In the former arrangement, only the front of the tool including the workpiece I/O port is maintained in the cleanroom environment of class 1 or better. In a ballroom configuration, the tools are arranged in clusters according to the operations they perform, with the entire tool being maintained in the cleanroom environment of class 1 or better.
Tools within a wafer fab include a front end interface which houses components that facilitate and monitor the transfer of wafers and other workpieces between the pods to the tools. A conventional front end unit 20 is shown in FIGS. 1 and 2. The unit 20, which is generally constructed at a tool manufacturer and then shipped to a wafer fab, includes a generally square or rectangular housing 22 which is affixed to the front of a tool. A front end unit 20 generally includes a workpiece handling robot 24 mounted within the housing and capable of r, θ, z motion to transfer workpieces between the workpiece carriers, tool and other front end components. The robot is generally mounted within the housing with leveling screws that allow the adjustment of the planarity of the robot once the unit 20 is constructed and affixed to a tool.
In addition to a robot 24, front end unit 20 generally includes one or more prealigners 26 for performing the operation of wafer center identification, notch orientation, and indicial mark reading. The prealigner(s) 26 are bolted into the housing 22 with leveling screws allowing the planarity of the prealigner(s) to be adjusted once the unit 20 is constructed and affixed to a tool.
The front end unit 20 further includes one or more load port assemblies 28 for receiving a workpiece carrier, opening the carrier, and presenting the workpieces to the robot for transfer of the workpieces between the carrier, prealigners and tool. For 300 mm wafer processing, a vertically oriented frame, commonly referred to as a box opener-loader tool standard interface (or “BOLTS” interface), has been developed by Semiconductor Equipment and Materials International (“SEMI”). The BOLTS interface attaches to, or is formed as part of, the front end of a tool, and provides standard mounting points for a load port assembly to attach to the tool. U.S. Pat. No. 6,138,721, entitled “Tilt and Go Load Port Interface Alignment System,” to Bonora et al. discloses a system for adjusting a load port assembly to the proper position adjacent a BOLTS interface and then affixing the load port assembly to the interface. This patent is assigned to the owner of the present invention and is incorporated by reference in its entirety herein.
Once the robot 24, the prealigners 26 and load port assemblies 28 have been mounted to the housing 22, the front end unit 20 is shipped to the wafer fab and affixed to a tool within the fab. After being properly secured to the tool, the front end components are leveled within the housing 22 via the leveling screws, and the robot is then taught the acquisition and drop-off positions it will need to access for workpiece transfer between the load port assemblies, the prealigners and the tool. A system for teaching the various acquisition and drop-off positions for the robot within the tool front end is disclosed in U.S. patent application Ser. No. 09/729,463, entitled “Self Teaching Robot,” which application is assigned to the owner of the present application and which application is incorporated by reference herein in its entirety. Once the robot positions have been taught, side panels are attached to housing 22 to substantially seal the housing against the surrounding environment.
As described above, conventional tool front ends include a plurality of separate and independent workpiece handling components mounted within an assembled housing. The housing includes a structural frame, bolted, constructed or welded together, and a plurality of panels affixed to the frame. After the housing is assembled, the front end components are affixed to the various panels. It is a disadvantage to prior art front ends that the overall system tolerances are compounded with each frame member, panel and component connection. The result is that the assembled front end components are poorly aligned and need to be adjusted to the proper position with respect to each other. The robot must also be taught the relative positions of the components so that the front end components can interact with each other. This alignment and teaching process must take place every time there is an adjustment to one or more of the front end components.
A further shortcoming of the prior art is that front end components are frequently made by different suppliers, each with its own controller and communication protocols. Steps must be taken upon assembly of the front end so that the controllers of each component can communicate with each other and the components can interact with each other. The separate controllers also complicate maintenance and add to the parts and electrical connections provided in the front end. Further still, especially in a ballroom configuration, the conventional front end unit takes up a large amount of space within a class 1 cleanroom environment where space is at a premium.